Is this the final ultrasound you will have? I'd wait until it was a little clearer. She's probably right (about the baby being a girl) because boys are so obvious that there is rarely any doubt. But if you're only in your mid pregnancy, you have time for her to get another look.
I would not set up for both maybe lean towards neutral colors. But I would Def try to have them look again
Could always get a 3D gender determination done, they average about $70
You can go to a place that only does gender checks not a hospital. Just Google places that do gender checks an it's less then $100